/Engine/Source/Runtime/AudioMixer/Public/AudioMixerSubmix.h
Down mix the given buffer to the desired down mix channel count.
static void DownmixBuffer ( const int32 InChannels, const [FAlignedFloatBuffer](API\Runtime\SignalProcessing\DSP\FAlignedFloatBuffer) & InBuffer, const int32 OutChannels, [FAlignedFloatBuffer](API\Runtime\SignalProcessing\DSP\FAlignedFloatBuffer) & OutNewBuffer )